If you cannot remember the date of your last menstrual period, or if you conceive without a period while breastfeeding, you can use ultrasonography to help estimate the number of days of pregnancy. The expected date of delivery can also be calculated from the first day of the last menstrual period, which is the first day of menopause. From the first day of the last menstrual period, it is usually nine months and seven days, which is the time of the due date, usually 40 weeks of gestation. 40 weeks of gestation, 21 days early, which means that the fetus is full term at 37 weeks of gestation. The delivery within two weeks after the due date is considered a normal delivery, and the delivery within 37-42 weeks of gestation is called a normal delivery, if it is less than 37 weeks of gestation, it is a premature delivery, and if it is more than 42 weeks of gestation, it is a premature delivery.